You get zekrom when you have beatin the 8 gym badges and beat the elite 4 but when you get to the champion Alder suddenly N`s castle crashes in and then you can get zekrom in N`s castle and then when you capture zekrom youwill hae to battle N and when you beat him you will battle ghetsis if you beat him you will be free and then you can go catch Terakkion,Virizion,Cobalion,thundarus, and Kyerum.